Thermal comfort is a major issue in cities and it is expected to change in the future due to the changing climate. The objective of this paper is to use the universal thermal comfort index (UTCI) to compare the outdoor thermal comfort in Hong Kong in the past (1971-2000) and the future (2046-2065 and 2081-2100). The future climate of Hong Kong was determined by the general circulation model (GCM) simulations of future climate scenarios (A1B and B1) established by the Intergovernmental Panel on Climate Change (IPCC). Three GCMs were chosen, GISS-ER, GFDL-CM2.1 and MRI-CGCM2.3.2, based on their performance in simulating past climate. Through a statistical downscaling procedure, the future climatic variables were transferred to the local scale. The UTCI is calculated by four predicted climate variables: air temperature, wind speed, relative humidity and solar radiation. After a normalisation procedure, future UTCI profiles for the urban area of Hong Kong were created. Comparing the past UTCI (calculated by observation data) and future UTCI, all three GCMs predicted that the future climate scenarios have a higher mode and a higher maximum value. There is a shift from 'No Thermal Stress' toward 'Moderate Heat Stress' and 'Strong Heat Stress' during the period 2046-2065, becoming more severe for the later period (2081-2100). Comparing the two scenarios, B1 exhibited similar projections in the two time periods whereas for A1B there was a significant difference, with both the mode and maximum increasing by 2 °C from 2046-2065 to 2081-2100.